1. Field of the Invention
This invention relates in general to satellite telecommunication systems and particular wherein the satellites have geostationary positional loops and consist of several satellites of identical telecommunication functions which orbit on circular or elliptical paths which are inclined relative to the equatorial plane.
2. Description of the Prior Art
In telecommunication satellite systems using geostationary orbit positions, communication earth stations can remain permanently directed to a satellite or, respectively, to a position and can operate telecommunications traffic in sequence without interruption. The unavoidable slight positional deviations of the satellite are compensated by means of follow-up by the communication earth station antennas.
Systems with geostationary telecommunication satellites which are positioned on geostationary orbits in equatorial plane are known. It is also known how to create quasi-stationary orbit positions north and south of the geostationary orbit with the assistance of a plurality of so-called geosynchronous satellites which have orbital nodes that lie on the same orbit position. These positions are successively assumed and reached by the participating satellite in stratified operation. For the purpose of radio-engineering decoupling, satellites which are underway between the quasi-stationary positions are switched as discussed in the publication International Telecommunications Union of Geneva CCIR 4/71-E. For reasons of orbital and radio-engineering necessities, both geostationary satellites as well as geo-synchronous satellites with quasi-position are situated on or very close to the geostationary orbit. The exploitation of this small belt around the earth for geostationary telecommunication satellite systems will become significantly overcrowded in the future. Also, the geostationary belt has the disadvantage that for countries which lie far to the north or far to the south of the equator due to the low elevation angle, the electromagnetic waves must travel a long path through the atmosphere thus having a negative effect on the quality and reliability of the satellite connections at higher frequencies. Also, systems with a plurality of orbiting telecommunication satellites are known which have the advantage of being able to service northern and southern countries (Molnia Program, Soviet Union), but however, these systems have the disadvantage in that the participating satellites wherein one terminates its service and the next begins its service simultaneously are not approximately located at the same point of the celestial sphere at the changeover time. This results in that either the associated earth station must be equipped with two antennas or operations must be temporarily interrupted during the changeover.
An additional disadvantage with known geostationary as well as traditional orbiting satellites lies in the fact that if one does not wish to accept considerable down times a backup satellite must be available for every satellite in an orbit close to the operating satellite.